In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 11, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 12(a), the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 12(b), or, as shown in FIG. 12(c), by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIG. 12.
Therefore, the 3 rd Generation Partnership Project (3GPP) and the 3 rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
As shown in the non-patent document 1, a conventional mobile communication system using “EUL” is configured to; increase a transmission rate of uplink user data when the mobile station UE has received a Relative rate Control Channel (RGCH) from a radio base station Node B. The RGCH indicates that the transmission rate of uplink user data should be increased (including “Up” command).
Further, as shown in the non-patent document 1, HARQ scheme has been adopted to the conventional mobile communication system using the “EUL”. Therefore, the radio base station Node B is configured to; transmit an affirmative transmission acknowledgement signal (Ack) to the mobile station whenever the reception and decoding process for each transmission data block forming the uplink user data has been successful, and to transmit a negative transmission acknowledgement signal (Nack) to the mobile station when the reception and decoding process for the transmission data block has not been successful.
The mobile station UE is configured to repeat transmitting the same transmission data block until the mobile station UE receives an affirmative transmission acknowledgement signal (Ack) or until the number of transmission reaches the maximum number of retransmission determined by the radio network controller RNC.
Here, when the “Up” command has been received through the RGCH, the mobile station UE is configured to increase the transmission rate of uplink user data, regardless of the “Ack/Nack/DTX” signal transmitted through an HICH.
In addition, the radio base station Nod B is configured to determine increase/decrease of the transmission rate of uplink user data, regardless of the reception and decoding process result of the transmission data block, so as to notify the determined result (ie., the “Up” command or the “Down” command) to the mobile station UE through the RGCH.
However, in the conventional mobile communication system using “EUL”, there has been a problem that the radio base station Node B may not be able to allocate necessary hardware resources for performing reception and decoding process for the retransmitted transmission data block, when a transmission rate of uplink user data transmitted from the mobile station UE has increased regardless of the negative transmission acknowledgement signal (Nack) transmitted from the radio base station Node B.    (Non-patent Document 1) 3GPP TSG-RAN TS-25.309 v6.2.0